Uhh, actually, trolling was originally a form of gag which is performed by starting a topic done to anger people, such as "Euthanasia should exist", but using reasons like "NOT EVERYONE SHOULD LIVE" and "OLD PEOPLE ARE ANNOYING ANYWAY, WHAT DO THEY DO FOR THE WORLD?"
"Cornering someone in a debate" is.... Winning an argument. That's... That's not trolling at all.

when I first started hearing the term "trolling" on the internet it was a word used to describe people who spam and post annoying things on forums. The term changed to rustling jimmies in a clever and funny way only later on.

When the internet thought the guy who was pissing everyone off was pretty cool and thought "Hey, if he can do it, why can't I?"
Thus, Reddit, 9fag, Funnyjunk, Tumblr, and other sites that dwell the species of newfag, had risen.